Aurora Borealis

By: Bill, Aubrey, Peter

INTRODUCTION

The aurora has fascinated, and often terrified, humans for thousands of years. From ancient times, tales and narratives about the aurora have been told by polar explorers, adventurers, fur traders, and early settlers.

Early researchers came up with many theories and scientific explanations for the aurora. They wondered if it was reflected firelight from the edge of the world, sunlight reflected from arctic ice, or maybe reflected light from ice crystals high in the sky.

It was not until the middle of the 19th century did scientists begin to make headway in the study of the aurora, and there are still many unanswered questions about it. Indeed, the aurora has provided one of the most challenging problems encountered in modern science.

Aurora science contributes greatly to space exploration, the development of high-tech industries, even to our everyday life. Auroras are a high latitude phenomenon; they are rarely seen at low latitudes.  This is why people living in the tropics and the subtropical regions are unfamiliar with these spectacular light shows in the night

The Aurora seen from the Space Shuttle

HOW HIGH IN THE SKY IS THE AURORA LOCATED?

The aurora hangs as a curtain-like structure high in the sky. The bottom edge of the auroral curtain is about 100 km (60 miles) above Earth. This altitude is about 10 times higher than the cruising altitude of a jumbo jet, and about one-half the orbiting altitude of the space shuttle.

Most weather phenomena occur well below the aurora. Although the aurora occurs high above Earth, the auroral curtain often appears to touch the ground or reach a mountain top. This is simply a matter of visual perspective, similar to the perspective that occurs when telephone poles of the same height look shorter in the distance.

WHERE CAN YOU SEE THE AURORA?

Early auroral scientists carefully counted the number of nights each year the aurora can be seen at a number of locations. They discovered that the aurora can be seen about 100 nights each year along an imaginary line connecting central Alaska, northern Canada, offshore from the southern tip of Hudson Bay, offshore from the southern tip of Greenland, northern Scandinavia, and along the arctic coastline of Siberia. By contrast, they learned that the aurora can be seen about 10 nights each year from Boston, New York, London, and Moscow, and about 1 night each year from San Francisco and Paris. Near the northern tip of Hokkaido, Japan, the aurora can be seen 0.1 night each year, or about once every 10 years..

WHAT KIND OF LIGHT DOES THE AURORA EMIT? What kind of light makes up the dancing aurora? To answer this question, Anders Angström, a Swedish physicist, used a prism to study auroral light during the middle of the last century. He discovered that auroral light is quite different than light emitted by the sun. Unlike solar light, which bends through a prism as a continuous beam gradating from red to violet light, auroral light consists of many lines and bands.

Auroral light is created by a process similar to that taking place inside a neon sign in a store window. In the thin tube of a neon sign, a high-vacuum electrical discharge flows from one end to the other with the help of high-speed electrons. When discharge electrons collide with neon atoms, they emit reddish light unique to the neon atom.

Auroral light occurs when high-speed discharge electrons collide with atoms and molecules in the upper atmosphere. Different kinds of atoms and molecules produce different colors of lights. The

common greenish white light in an auroral display is produced by collisions with atomic oxygen. The

beautiful pinkish light is emitted by molecular nitrogen.

Pinkish light from molecular nitrogen at

the bottom of an auroral curtain

Greenish-white light from atomic oxygen

AURORAL LEGENDSEvery northern culture has oral legends about the aurora, passed down for generations. The Eskimos, Athabaskan Indians, Lapps, Greenlanders, and even the Northwest Indian tribes were familiar with this mysterious light in the sky. Ancient Eskimo stories often are associated with notions of life after death. Some thought that the aurora was a narrow and dangerous pathway for the departed souls to heaven. Others thought that the aurora was the collective image of spirits playing football with the skull of a walrus. Many feared whistling toward the aurora, because they believed that a whistle would cause the aurora to come down and fetch them.

In medieval days, people feared the dark red glow of the aurora because

they believed it to be a bad omen.

Medieval depiction of a red aurora

The aurora also was associated with battles or depicted as candles in the sky in medieval artwork.

THE AURORA’S Most POLAR EXPLORERS

Sir John Ross

Sir John Franklin

Fridtjof Nansen

Sources

Lummerzheim, Dirk. Aurora FAQ. September 19, 2010. http://odin.gi.alaska.edu/FAQ/. March 3, 2011.

Asahi Aurora Classroom. University of Alaska Fairbanks. August 2003. http://www2.gi.alaska.edu/asahi/aurfaq.htm March 1, 2011.

Aurora Page. Michigan Technology University. June 22, 2010. http://www.geo.mtu.edu/weather/aurora/. March 4, 2011.